1. Field of the Invention
This invention relates to high security or nonpickable locks having a housing, a key plug rotably mounted in said housing, tumbler means for blocking rotation of said plug unless set at a predetermined position by insertion of a properly bitted key, and means designed to prevent picking of the lock device.
2. Description of the Prior Art
Locks in which a key plug is rotably mounted within a cylinder and which are released for rotation upon the setting of a series of tumblers in a predetermined position are well known. Furthermore, the problems associated with designing and manufacturing a nonpickable lock of this type have long been recognized by those skilled in the art.
Prior art devices intended to be nonpickable have been devised, but have not proved to be entirely functional. In some cases the locks have been so complex as to be incapable of being manufactured economically. In other cases the locks have become inoperative after only moderate use. Other supposedly nonpickable locks require the employment of keys of complex shapes, making duplication of the keys impossible with the equipment normally available to a locksmith. Most importantly, many of such locks have not proved to be nonpickable.
Because such problems are well known a number of nonpickable locks have been known in the art for some years. For example, U.S. Pat. No. 3,590,615 discloses an antipick lock. This apparatus utilizes lock pin tumblers equipped with one or more side pins, each of which is in cam relation to one or two tumblers so that the tumblers when moved by their spring pressure to a locking position will cause the side pins to project beyond a side of the key plug. Picking torque that may be applied to the key plug then will be transferred through the side pins to the cylinder. Also, a tumbler or coacting side pin alternately will move into a portion of the keyway during an attempt to pick the tumblers.
Another pickproof lock is disclosed in U.S. Pat. No. 3,455,130. That apparatus discloses pin tumblers in combination with a sidebar normally extending from the plug into a slot in the housing, thus preventing rotation of the plug. When a proper key is inserted into the keyway, the tumblers are configured so as to allow the side bar to move inwardly, allowing rotation of the lock. Each and every tumbler must be properly positioned in order for the side bar to release the plug.
Still another device, U.S. Pat. No. 2,295,737, discloses a pickproof lock utilizing a locking element for locking the key plug against rotation relative to the cylinder. The locking element locks the key plug against full rotation, while permitting some free rotation thereof. The locking element is mounted for movement to release the key plug for full rotation in the event that a series of tumblers are properly aligned by a key.
In addition to the device discussed above, a number of key operated cylinder locks have been developed. These devices generally comprise a housing, a cylinder having a keyway and a series of tumblers. No means specifically designed to prevent picking of these locks is disclosed.
Examination of the existing art reveals a number of pickproof locks. Unfortunately, many of these are extremely complex in that the antipick devices actually perform the function of blocking rotation of the cylinder. Many separate moving parts are required, each of which must be carefully machined and assembled if the lock is to work properly. Many of these locks, because of their complex construction, have not been able to withstand the rigors of prolonged, frequent usage. Still others have proved to be ineffective for their failure to provide a truly pickproof lock.
Thus, despite the large number of locks available, the conventional pickproof lock is generally costly in terms of manufacture and rate of failure.